This invention relates to a method and apparatus for gas phase synthesis and, in particular, to a method of synthesizing in gas phase a functional material or a hard film, especially a diamond film to be used for mechanical purposes and for semiconductor purposes, as well as to an apparatus for carrying out this method.
As a representative example of a conventional apparatus for gas phase synthesis of a diamond film, there are known those as disclosed by S. Matsumoto et al in the Japanese Journal of Applied Physics, vol. 21, p. L183 (1982); M. Kamo et al in the Journal of Crystal Growth, 62, p. 642 (1983); K. Suzuki et al in the Applied Physics Letters, 50, p. 728 (1987).
In case the diamond film is used as a coating film on a tool or a wear-resistant sliding part, the adhesion of the film to a substrate is an important matter of interest. This matter is known to be solved by controlling or increasing the density of nucleation of the diamond crystal nuclei grown at the beginning on the substrate.
Further, in case the diamond film is used as a protection film on an optical window or a protection film of a lens, it is necessary for the film surface to be smooth in order to improve the light penetrating characteristics by minimizing the scattering of light on the film. However, since the diamond grows in the form of nuclei, the surface of the diamond film formed cannot be made smooth if the density of the nucleation is small. Therefore, in this case, it is also necessary to control or increase the density of nucleation of the diamond crystal nuclei.
In case the diamond film is used for semiconductor purposes, it is necessary to epitaxilly grow the diamond film. For this purpose, it is required that the film be formed under conditions of high density of growth of crystal nuclei, i.e., high density of nucleation.
As described above, controlling or increasing the density of nucleation is especially important in utilizing the material susceptible of easy nucleus growth such as diamond as a functional material or as a hard film.
On the other hand, it is sometimes disadvantageous from a viewpoint of other film characteristics or economy to unnecessarily increase the density of nucleation. In such a case, it is important to control the density of nucleation at a level above a predetermined value while satisfying the other requirements.
As a method of controlling or increasing the density of nucleation, there is known, at present, a method of scratching the substrate on which the film is formed with diamond powders prior to the film formation (as disclosed, for example, by Yugo et al in the Extended Abstracts of the 35th Spring Meeting of the Jpn. Soc. Appl. Phys. and the Related Societies, p. 438, 1988).
This method of scratching treatment with diamond powders is a method in which prior to film formation a substrate is placed into a solution containing therein diamond powders outside a synthesizing apparatus and subject it to ultrasonic vibrations for a predetermined period of time, or the substrate is rubbed against diamond powders to form very fine scratches on the substrate. Thereafter, the film is formed on the substrate. According to this method, by controlling the density of the scratches to be formed on the substrate, the density of nucleation can be controlled to a certain degree within a range of 10.sup.5 to 10.sup.9 /cm.sup.2.
The evaluation of the density of nucleation of the diamond nuclei has generally been made by taking out a sample, after film formation, to examine with an electron microscope or the like, thereby counting the number of grown nuclei within a predetermined area.
Since the control or the evaluation of the density of nucleation according to the conventional method is carried out only before or after the film formation, the grasping of the density of nucleation is nothing but an estimate or a result. Therefore, it was impossible in the conventional method to accurately control the density of nucleation.
Further, in case the number of grown nuclei is counted in process with an electron microscope, the electron microscope must be placed inside an apparatus for gas phase synthesis. It is impossible to count the number in such a high-pressure zone as in the method of gas phase synthesis because the mean free path of the electrons is short.